RF-MEMS switching devices have two stable states just like semiconductor RF switches (for example, PIN diodes or GaAs FET switches). Switching between the two states is achieved through the mechanical displacement of a freely movable structural member (i.e., the armature). The displacement is induced via a micro-actuator for which various actuation mechanisms exist including, electrostatic, electrothermal, piezoelectric, and electromagnetic means.
The majority of RF-MEMS switches rely on electrostatic actuation, which is based on the attractive Coulomb force existing between charges of opposite polarity. Electrostatic drive offers extremely low power consumption, in which power is consumed only during switching (compare a digital inverter stage). Other advantages of using electrostatic actuation are the relatively simple fabrication technology, which is much simpler as compared to, for instance, electromagnetic excitation; the high degree of compatibility with a standard IC process line; and the ease of integration with planar and micro-strip transmission lines.
RF-MEMS switches implementing electrostatic actuation are currently the best-developed RF-MEMS component and have been demonstrated on a laboratory scale by a number of companies and academic institutions from all over the world. A first clear wave of scientific publications and patents appeared halfway through the nineties, with clearly increased interest marked since the late nineties. The literature undoubtedly indicates the key advantages of RF-MEMS switches as compared to semiconductor solutions (e.g., GaAs FETs, PIN diodes).
However, known RF-MEMS devices have one major disadvantage, namely the risk of self-actuation when the RF signal reaches a high power and generates an RF induced force.
From U.S. Patent Application Ser. No. 2003/042117, U.S. Patent Application Ser. No. 2004/000696, and European Application No. EP 0709911, MEMS devices are known in which there is a lateral offset between a region of maximum actuation liability on the collapsible portion of the device (bridge or cantilever structure) and a conductor on which a signal can be applied. This lateral offset results from the fact that the devices are designed with the goal of achieving a reduced actuation voltage.